Previously, epoxy resins have been generally used for optical devices or material for optical parts, particularly encapsulant for light emitting diode (LED) elements. Silicone resins also have been tried to use as molding material for LED elements (see Patent Document 1, Patent Document 2) or as material for color filters (see Patent Document 3), however, they are scarcely used practically.
Recently, due to attention paid to white LEDs, there arise problems about epoxy encapsulant such as yellowing by ultraviolet ray etc. and cracks caused by increasing calorific values due to miniaturization, which were not regarded as a problem previously and are pressing needs to be handled. As a countermeasure, it has been examined to use a cured product of a silicone resin having a large amount of phenyl groups in the molecule.
As the substrates for present LED use, however, silver substrates are mainly used. Silver is corroded by sulfur compounds in the air, which can lower the emission efficiency of LED in some cases. This phenomenon can be suppressed by cured product of the foregoing silicone resin having phenyl groups in a certain but less degree compared to conventional epoxy encapsulant.
As the countermeasure, it has been proposed a material which can compatible resistance to heat and corrosion of silver by using a curable composition having a polycyclic hydrocarbon group (see Patent Document 4). This composition, however, has a transition point as a resin near the room temperature, and accordingly has a problem to generate cracks due to temperature change to high temperature or low temperature.